©2004 CRC Press LLC 6 Kinetics of the Ozonation of Wastewaters The application of ozone is not addressed solely to the treatment of natural waters for the preparation of drinking water. For a long time ozone has been applied to the treatment of wastewater. Although the general objective of ozonation in waste- water treatment is disinfection after the secondary biological treatment 1,2 ozone also plays a variety of other roles, mainly to improve the efficiency of other unit operations such as coagulation–flocculation–sedimentation 3,4 or carbon filtration; 5,6 remove biologically refractory or toxic compounds to improve biological oxidation units, 7,8 or reduce the amount of sludge generated in these latter systems. 9,10 Specific literature concerning the application of ozone in the treatment of wastewater (mainly industrial wastewater) dates back to the 1970s, when Rice and Browning 11 pub- lished a compendium of cases of ozone application. Thus, industries related to both inorganic and organic compounds have used ozone for decontamination or disin- fection purposes. Rice and Browning 11 classified these industries in 21 categories as listed in Table 6.1. Also, other wastewater such as those produced in the pesticide manufacturing and use, rinsing of wood chips contaminated with pentachlorophenol or other wastes containing 1,4-dioxane, marine aquaria, swine marine slurries from stored livestock wastes, leachates, etc., have been treated with ozone. 12–17 Among the numerous industrial wastewater mentioned, ozone is specially applied to those containing phenols that are present in numerous industrial processes (coke plants, petroleum refinery, plastics, pulp and paper, textiles, soaps and detergents, food and beverage, etc.). Other wastewater containing surfactant compounds and dyes have also been treated with ozone. 18,19 In Table 6.2 a list of recent papers of the last 7 years dealing with the use of ozone in wastewater treatment is presented. Many compounds present in most of these wastewaters do directly react with ozone in reactions with very high rate constants. Thus, one expects that ozone is a truly recommended oxidant to reduce or even eliminate the contamination of these wastewater. However, a rather different result would be obtained if ozonation is applied as the main operation to decontaminate wastewater. The problem of ozone use in wastewater arises from two facts: the high concentration of fast ozone reacting compounds (phenols, dyes, some surfactants of benzene sulphonate acid type, etc.) and the presence of other substances (i.e. salts, carbonates, etc.). On one hand, the high concentration of fast ozone reacting compounds makes mass transfer limit the ozonation rate (see later Table 6.3) and, on the other hand, the presence of ozone decomposition–inhibiting compounds or hydroxyl free–radical scavengers stops the ozonation rate when ozone indirect reactions are the main way of pollutant ©2004 CRC Press LLC removal (a situation that happens when the concentration of fast ozone-reacting compounds have been reduced so that the kinetic regime of their ozonation reactions becomes slow). As a result, ozonation is not usually a cost-effective technology if used as the main treatment operation of wastewater due to the high amount of ozone needed. As a consequence, ozone is recommended in wastewater treatment as a complementary agent of other processes to mainly increase biodegradability, reduce toxicity of recalcitrant compounds, etc. 67 TABLE 6.1 List of Wastewater Treated with Ozone According to Rice and Browning 11 Industry Objectives or Compounds Present Aquaculture Shellfish depuration, marine water quality, disease prevention, toxicity Electric power manufacturing Biofouling control Electroplating Removal of cyanides and cyanates. Metal complexe cyanides with O 3 /UV Food and kindred products Sterilization of water for bottle washing, COD reduction of brines, disinfection of processing water Hospital wastewater Shower, operating room, kitchen, chemical lab, x-ray lab. Target COD for water reuse = 10 mgL –1 Municipal wastewater, Inorganics containing water Chloro–alkali production Removal of Fe and Mn, heavy metals: Hg, Cr(III), ammonia (among others) Iron and steel, coke plants Cyanides, cyanates, phenols, sulfide (among other) Leather tanneries Removal of colorants, sulfide Organic chemical manufacturing plants Salicylic acid, caprolactam synthesis, alkylamines, organic dyes, chelating agents, etc. Paints and varnishes Phenols, methylene chloride Petroleum refineries Oils, hydrocarbons, nitroaromatics, phenols, ammonia, mercaptans, etc Pharmaceutical industries Little information available Photoprocessing Surfactants, sulfate, phosphates, cyanates, heavy metals Plastics and resins Phenol, formaldehyde, synthetic polmers (unsaturated organics, alkylnaphthalene sulfonates), leathers (Zn, phenols.), rubber (olefins, mercaptans.) Pulp and paper Bleaching, odor control, mill wastewater treatment, spent sulfite liquor treatment Soaps and detergents Alkylbenzene sulfonate surfactants, reduce foaming Textiles Organic dyestuff, sizing agents, surfactants, organic and inorganic acids, azoic dyes, azobenzenes a Phenols were also classified as an independent group due to their importance in many wastewater treatment industries as shown above. Source: From Rice, R.G. and Browning, M.E., Ozone Treatment of Industrial Wastewater , Noyes Data Corporation, Park Ridge, N.J., 1981. ©2004 CRC Press LLC TABLE 6.2 Recent Literature concerning Works on Wastewater Ozonation Wastewater Type Reacting Features Reference # and Year Textile and dye effluent combined with domestic effluent Pilot plant system: 3 contact columns, pH 7–7.4, Anionic surfactants and non-ionic detergents: 3–4 , COD: 150–200 19, 1995 Pulp mill effluents Batch and semicontinuous ozonation, Filtrate bleaching process wastewater COD = 3060, BOD 5 = 540, pH 9.65; Aerated stabilization basin wastewater: COD = 1440, BOD 5 = 25, pH 7.1 20, 1995 Oil shale Semibatch ozonation, pH 10, COD: 4000, BOD 5 /COD: 0.23, Phenols: 450, O 3 /H 2 O 2 , and other AOP tested 21, 1995 Mechanical and chemical pulp mill Semibatch ozonation, pH 7 (adjusted). Different effluents: COD: 1723–615, BOD: 281–708, Toxicity reduction 8, 1996 Printed circuit board rinse water Batch ozonation, Compounds: thiourea, Na gluconate, nitrilotriacetic acid, COD: 45, TOC: 13, O 3 /H 2 O 2 and catalytic ozonation 22, 1997 Swine manure wastes Semibatch ozonation, COD: 54200, BOD 5 : 29800, pH 7, Compounds present: Volatile fatty acids, phenolics, indolics, ammonia, sulfide, phosphates 23, 1997 Pharmaceutical effluents AOP treatments: Fenton, O 3 /UV, H 2 O 2 /UV, semibatch ozonation, COD: 670–2700, AOX: 3–5 24, 1997 Boiling feed water in power plant Real water treatment plant, pH 6.3–7, COD: 1–10, TOC: 1.5–4, Fe, Mn, chlorides, sulfates, nitrates. O 3 , and O 3 /H 2 O 2 25, 1997 Dental surgery Disinfection 26, 1997 Dyes Pilot plant, COD: 1071, BOD: 348, Ammonia: 21, different dyes: reactive, disperse, sulfur, acid, direct 27, 1998 Landfill leachates Semibatch ozonation, COD: 45000–700, pH 5.4–6 16, 1998 Domestic plus industrial Coagulation aid, COD: 480, TSS: 110, pH 8.4 28, 1998 Sewage Reduce sludge production, TOC: 200, MLSS in aeration tank: 1500–2500; intermitent and continuous ozonation 9, 1998 Municipal Pilot plant ozonation, UV, O 3 , peracetic acid, Disinfection, economics, pH 6.7–8, DOC: 3–24 29, 1999 Membrane Textile effluent Batch ozonation, COD: 595, BOD 5 : 0, pH: 7.95, non-ionic surfactants, aldehydes 30, 1999 Synthetic dyehouse effluent 40-fold diluted dyebath: DOC: 25, pH: 10.94, different dyes and also: urea, chloride, carbonate. O 3 , O 3 /H 2 O 2 , H 2 O 2 /UV, Semibatch ozonation 13, 1999 Sludge reduction Sludge ozonation to solubization, 31, 1999 Table olive Semibatch ozonation, Different AOP (O 3 , O 3 /H 2 O 2 , O 3 /UV), COD: 19–25, BOD 5 : 2–4.3, pH 13, Biodegradability variation 32, 1999 Textile Semibatch ozonation, O 3 , O 3 /H 2 O 2 , COD: 320, BOD 5 : 42–64, pH 8.2 33, 1999 Domestic Continuous pilot plant ozonation plus biological aerobic oxidation, COD: 294, BOD 5 : 170, pH: 7.2–7.6 34, 35, 1999 ©2004 CRC Press LLC TABLE 6.2 (continued) Recent Literature concerning Works on Wastewater Ozonation Wastewater Type Reacting Features Reference # and Year Wine distillery plus domestic sewage Semibatch ozonation plus biological aerobic oxidation, COD: 21700–300, BOD 5 : 13440–187, pH 5.4–10, Kinetic study, biodegradability 36, 37, 1999 Domestic Batch ozonation, COD: 380, BOD 5 : 218, pH: 7.6, Improve sedimentation 38, 1999 Domestic Semibatch pilot plant, pH 7.6–8.6, DOC: 7–16, Bromide: 3.48–10.1, Total coliforms: 1380–4550. Disinfection for reuse in agriculture 39, 2000 Pharmaceutical Semibatch ozonation. O 3 , O 3 /H 2 O 2 , Different compounds: acetylsalicilic, clofibric acid, diclofenac, ibuprofen: 2 µ gL 1 , pH 7, 10ºC 40, 2000 Pulp mill Batch and semibatch ozonation, pH 2–10, Ethylenediaminetetracetic acid (EDTA): 10–1000 41, 2000 Sludge from anaerobic degradation Batch and continuous ozonation, Reduce sludge by partial oxidation, TCOD: 7900, TOC: 2900, SS: 9000 42, 2000 Dyeing and laundering Dyeing: Anionic detergent: 142, COD: 440, chlorides: 8000, pH 7.5, Laundering: COD: 1650, anionic detergents: 110, Non-ionic detergents: 680, pH 10. Different AOP treatments 43, 2000 Agroindustrial-domestic Continouous pilot ozonation plus aerobic biological oxidation, COD: 2250, BOD 5 : 1344, pH: 3–7 44, 2000 Table olive plus domestic Semibatch ozonation plus aerobic biological oxidation, COD: 1110, BOD 5 : 570, Nitrites, ammonia n-phenolics, pH 11.1 45, 2000 Olive oil and table olive plus domestic Semibatch pH sequential ozonation, Olive oil ww: COD 1465, BOD 5 : 1240, pH 5.8; Table olive ww: COD: 1450, BOD 5 : 910, pH: 11.3, nitrites, ammonia, phenolics, Ozone with pH cycles 46, 2000 Petrochemical Ozone plus biological activated carbon. Wastewater: Benzoic acid and aminobenzoic acid: 500, acrylonitrile: 100, pH 7. 7, 2001 Manufacturing dyes Ozone as pretretment of biological oxidation, semibatch ozonation, 3-methyl pyridine: 10 –3 –10 –4 M, pH 4–6. Kinetic study 47, 2001 Cherry stillage (2 times diluted) Semibatch ozonation plus aerobic biological oxidation, COD: 145–180, BOD 5 100–140, pH 3.8 48, 2001 Wine distillery and domestic Semibatch pH sequential ozonation, Domestic ww: COD: 300, BOD 5 : 160, pH 7.6; Distillery ww: COD: 2500, BOD 5 : 1340, pH 3.5, Ozone with pH cycles 49, 2001 Landfill leachate Semibatch ozonation, pH 8.3, COD: 1400, BOD 5 : 170, SS: 270 50, 2001 Dyes production Semibatch ozonation, Different dyes, COD: 18400–2420, pH: 0.5–9.3 depending on the dye type. O 3 /H 2 O 2 and Fenton 51, 2001 Textile Different AOP treatments, Improve biodegradability, COD: 2154, BOD 5 : 1050, TOC: 932, Antraquinone, anionic detergent, alkylnaphthalensulfonate, chlorides 52, 2001 ©2004 CRC Press LLC TABLE 6.2 (continued) Recent Literature concerning Works on Wastewater Ozonation Wastewater Type Reacting Features Reference # and Year Domestic plus dyestuff Pilot plant ozonation, COD: 234–38, BOD 5 : 5.6–27, SS: 69–12, pH 7.1–7.7, Different dyestuff 53, 2001 Mechanical pulp production Semibatch ozonation, Wet air oxidation, COD: 1600–16500, TOC: 6100–6700, pH 4.8–6.5, tannin+lignin acids, fatty acids, sterols, triglycerides among others 54, 2001 Fruit Cannery effluent Semibatch ozonation, COD: 12000–45000, pH 9.8–13.5: O 3 , O 3 /H 2 O 2 , Activated carbon 55, 2001 Kraft pulp mill effluent Pilot plant impinging jet bubble ozone column, COD: 750–681, BOD 5 : 21.5–18.8, pH: 7.6, Aromatic halogen and color causing compounds 56, 2001 Secondary and terciary domestic effluents Pilot plant ozonation, COD: 30–71, TOC: 0 < 10–26, pH: 7–7.5, Different fecal microorganisms. Disinfection for reuse 57, 2002 Paper pulp effluents Semibatch ozonation, 10 different AOP applied, COD: 1384, TOC: 441, pH 10, comparison and cost estimation 58, 2002 Reactive dyebath effluent Semibatch ozonation, Comparison of AOPs (O 3 , UV/H 2 O 2 , UV/TiO 2 ), 15-fold dilution, TOC: 46.8, AOX: 0.102, carbonates: 490.6, pH 10.9, Different dyebath 18, 2002 Textile effluent Packed bed (raschig ring) ozone continuous flow column, COD: 1512, BOD: 90.6, pH 10.9. Reductions of COD, pH. Phytotocicity reduction. 59, 2002 Domestic sludge Cylindrical bubble column. MLSS: 10100 with 73% VSS. Ozone dosage: 0.01–2 g/gMLSS. Significant mineralization at high ozone dosage and solubilization at low ozone dosage 60, 2002 Fruit cannery (FC) and winery (W) effluents anaerobically treated After anaerobic oxidation: FC: COD: 525–750, W: COD: 148–370. Ozone and ozone/hydrogen peroxide treatment in continuous flow bubble column plus GAC adsorption in fixed bed column. COD and colour reductions followed. 61, 2002 Industrial landfill leachates Treatments: Ozone, ozone/hydrogen peroxide, hydrogen peroxide. Semibatch bubble column. Biological oxidation postreatment. BOD/COD = 0.05, COD: 390–560. Increases of biodegradability and up to 50% COD reduction. 62, 2002 Pharmaceutical effluent Semibatch bubble column, Values of biologically treated wastewater: COD: 8034, BOD: 3810, pH 8.7. Significant UV absorbance reductions. 63, 2002 Log yard run-off Pre- and post-ozonation of biological oxidation. Magnetically semibatch tank reactor. BOD: N: P: 100: 5: 1, MLSS: 2500: Ozone reduces COD (22%) and increases BOD (38%) 64, 2002 Domestic effluent Activated sludge ozonation. Sludge periodically treated with ozone in a semibatch tank. 75% reduction with 0.05 gO 3 /gVSS. Biological reactor: residence time: 10 d, 2 gL –1 SS. Slight increase of COD 65, 2002 ©2004 CRC Press LLC 6.1 REACTIVITY OF OZONE IN WASTEWATER In ozonation processes, the nature of compounds present in water will determine the degree of reactivity with ozone. Thus, compounds with specific functional groups (aromatic rings, unsaturated hydrocarbons, etc.) are prone to ozone attack while other compounds (saturated hydrocarbons, alcohols, aldehydes, etc.) can be consid- ered refractory to the ozone attack. In these cases, however, the second type of ozone reaction (indirect reactions) can play an important role, although this will also depend on the concentration of fast ozone-reacting compounds (kinetic regime) and hydroxyl radicals, and the way they are generated, inhibiting substances and pH of water. According to these comments, when ozone is applied to a real wastewater there will likely be numerous series-parallel ozone reactions depending on the wastewater complexity. If the presence of initiators, promoters, and inhibitors is of great impor- tance in the treatment of natural water, the unknown nature and concentration of these compounds and others that directly react with ozone constitute the main problem to study not only the kinetics of wastewater but also to predict ozonation efficiency. Knowledge of the composition of the wastewater results is fundamental to make any predictions about the ozone reactivity and potential application. In addition, pH and concentration of the compounds present in the wastewater are other key factors for further kinetic studies. The chemical composition of the wastewater determines its potential reactivity with ozone. Table 6.3 gives values of the Hatta number of some ozone direct reactions with compounds that could be present in wastewater and the kinetic regime of these ozonation processes. Also, information is given about the recommended ozone system that should be applied to improve as much as possible the pollutant removal rate. As can be deduced from Table 6.3 pH, concentration, and nature of pollutants are major factors affecting the recommended action. Some of these compounds dissociate in water when pH is increased, enhancing the ozonation rate (see Chapter 2). In these cases, mass transfer limitation constitutes the major problem and ozone feeding devices are key factors affecting the performance of the ozonation rate. Other compounds such as pesticides are usually present at low concentration (ppm or ppb level) due to solubility limitations. In these cases, chemical ozone reactions control TABLE 6.2 (continued) Recent Literature concerning Works on Wastewater Ozonation Wastewater Type Reacting Features Reference # and Year Pharmaceutical effluent Synthetic wastewater prepared from antibiotics. COD: 900, 1.5-L semibatch bubble column. Effects of pH and addition of hydrogen peroxide. Increases of BOD/COD 66, 2003 Units in mgL –1 ©2004 CRC Press LLC TABLE 6.3 Reactivity and Kinetic Regimes of Industrial Wastewater Ozonation Related to the Presence of Some Specific Contaminants Wastewater Type Specific Contaminant Concentration, pH and Rate Data Hatta Number, Kinetic Regime, and Action to Take Ash dump 21 Phenolics Hundreds of mgL –1 , pH = 12, k = 1.8 × 10 7 68 Ha > 10, Instantaneous, DW, AOP NR. Swine manure wastes 23 Odor compounds: p-cresol Sulfides Few to tens mgL –1 , pH 7, k = 7.5 × 10 5 (of O 3 -o-cresol reaction) 69] Tens of mgL –1 , pH 7, k = 3 × 10 9 70 Ha < 10, Fast to moderate regime, DW, AOP NR Ha > 10, Fast to Instantaneous regime, DW, AOP NR Pharmaceutical 24 AOXs: Chlorophenol Heptachlor Few mgL –1 , pH 7, k = 10 8 68] Hundreds µ gL –1 , pH 7, k = 90 71 3 < Ha < 10, Fast pseudo first order regime, DW, AOP NR Ha < 0.1, Slow regime, IW, AOP R Pulp mill 41 EDTA Hundreds mgL –1 , pH 8, k = 20000 (O 3 -dimethylamine reaction) 68 Ha < 0.5, Moderate regime, Mainly IW, AOP R Textile 18,43,52 Azoic dyes Few to tens mgL –1 , pH 10, k = 10 8 72 3 < Ha < 10, Fast regime, DW, AOP NR Table Olive 45 Phenolics Hundreds to thousands of mgL –1 , pH 12.9, k = 1.8 × 10 7 (O 3 -phenol reaction) 68 3 < Ha < 20, Likely fast regime, DW, AOP NR Olive Oil 46 Phenolics Thousands of mgL –1 , pH 4.9, k = 5 × 10 4 (O 3 -phenol reaction) 68 1 < Ha < 5, Moderate to fast regime, DW, AOP NR Petrochemical 7 Benzoic acid Hundreds of mgL –1 , pH 7, k < 0.15 (p-chlorobenzoic- O 3 reaction) 68 Ha < 0.01 Very slow regime, IW, AOP R Herbicide manufacturing Atrazine and others Tens to thousands µgL –1 , pH 7, k < 10 73 Ha < 0.01, Very slow regime, IW, AOP R Electroplating, photoprocessing 11 Cyanides Tens of mgL –1 , pH 10, k = 10 5 70 Ha < 3, Moderate regime, DW, AOP only for complex cyanides Petrochemical PAHs: phenanthrene Tens to thousands µgL –1 , pH 7, k = 3000 74] Ha < 0.01, Slow regime, IW, AOP R Municipal Ammonia Detergents: NaDBS Tens to hundreds mgL –1 , pH 7, k < 1 70] Few mgL –1 , pH = 7, k < 5 75 Ha < 0.001, Very slow regime, IW, AOP R Ha < 0.001, Very slow regime, IW, AOP R Explosives Nitrotoluenes Few mgL –1 , pH 7, k < 10 76 Ha < 0.01, Slow regime, IW, AOP R ©2004 CRC Press LLC the process rate, and advanced oxidation processes are recommended (i.e., O 3 /H 2 O 2 ). As will be shown in Chapter 7, when ozone reactions develop in the slow kinetic regime (chemical control) the indirect ozone reactions usually predominate. How- ever, the presence of hydroxyl radical scavengers needs to be considered as a limiting step. Also, the case of volatile compounds (benzene, toluene, trichloroethylene, etc.) is particularly important since volatility could constitute an important way of pol- lutant removal. For example, in some work 78 volatility constituted the main way of trichloroethane removal in an ozonation process. Then, in these cases caution should also be taken regarding the possible waste of ozone. Although ozone reactivity with single compounds present in wastewater (Table 6.3) can be predicted, classification of all wastewater regarding its reactivity with ozone is a rather difficult, if not unrealistic, task. However, as a general rule, high concen- tration of pollutants would suggest high reactivity with ozone (which is an indication of fast kinetic regime and ozone direct reactions) and low concentration usually means low ozone reactivity and, hence, a factor that favors the development of ozone indirect reactions. 6.2 CRITICAL CONCENTRATION OF WASTEWATER Because of the changing nature of compounds present in wastewater while undergoing ozonation (i.e., phenols becomes unsaturated carboxylic acids and then aldehydes, saturated carboxylic acids, ketones, etc.), the reactivity in terms of kinetic regime of ozonation usually changes from fast to slow. Knowledge of the critical concentration TABLE 6.3 (continued) Reactivity and Kinetic Regimes of Industrial Wastewater Ozonation Related to the Presence of Some Specific Contaminants Wastewater Type Specific Contaminant Concentration, pH and Rate Data Hatta Number, Kinetic Regime, and Action to Take Gasoline tank leaking Petroleum industry BTEX: Benzene, toluene, ethylbenzene, xylene Few µgL –1 , pH 7, k < 100 77 Ha < 0.001, Very slow regime, IW, AOP R Chemical processes 1,4-dioxane Hundreds µgL –1 , pH 7, k = 0.32 77 Ha < 0.001, Very slow regime, IW, AOP R Chemical industries: Groundwater Low molecular weight organohalogens: TCE, PCE, DCE Few to hundreds of µgL –1 , pH 7, k < 100 77 Ha < 0.001, Very slow regime, IW, AOP R Units of k in M –1 s –1 , Ha: Hatta number (k L = 5 × 10 –4 ms –1 and D O3 = 10 –9 m 2 s –1 to determine Ha). DW: Process through direct way of ozone, IW: Process through indirect way of ozone, AOP NR: Advanced oxidation process not recommended (see Chapter 7), AOP R: Advanced oxidation process recommended (see Chapter 7). ©2004 CRC Press LLC value of any wastewater to change from one degree of ozone reactivity to the other depends on the nature of the wastewater and can be known from laboratory exper- imental results. When ozone is applied to some wastewater in a semibatch well- agitated tank, the pollution concentration (measured as chemical oxygen demand, COD) vs. time data usually takes the trend plotted in Figure 6.1. In most cases, two reaction periods will be noted: the first initial period of high ozonation rate where the pollution concentration rapidly falls, and a second period where the ozonation rate is continuously decreasing with time until the ozonation rate is stopped with the pollution concentration reaching a plateau value. The critical pollution concen- tration would be that corresponding to the time when both periods coincide (about 10 min in Figure 6.1). In most cases, the pollution of wastewater during the first period is removed through direct ozone reactions that usually develop in the fast kinetic regimes of ozonation. In these cases, the absence of dissolved ozone is a clear indication that a fast or instantaneous kinetic regime of ozonation develops (see Chapter 4). For the second period, ozone likely decomposes in hydroxyl radicals and pollution is mainly removed through indirect ozone reactions. In this second period, ozonation reactions develop in the slow kinetic regime and removal of COD is carried out at a lower rate because carbonate/bicarbonate ions have been formed as a result of partial mineralization during the initial fast reaction period. It should be mentioned, however, that in some cases only one reaction period seems to develop, depending on the nature of wastewater as will be shown in section 6.4. In any case, and as a general rule, it can be said that high polluted wastewater ozonation is accomplished through fast kinetic regime ozone direct reactions, while low polluted wastewater ozonation develops through slow kinetic regime ozone indirect reactions. 6.3 CHARACTERIZATION OF WASTEWATER Through wastewater characterization, the nature of the reactions that ozone would undergo in the wastewater can be established. As shown above, the ozone reactivity depends on the concentration (and also nature) of pollutants present in wastewater. However, in FIGURE 6.1 Typical profiles of COD with time in ozonation experiments of industrial wastewaters showing the critical concentration point (values of COD and time in x and y axis present arbitrary values). Time, min 0 10 20 30 40 50 60 0 200 400 600 800 1000 COD, mgL –1 Critical point ©2004 CRC Press LLC real wastewater the actual pollution concentration is unknown and surrogate parameters (chemical oxygen demand, COD, total organic carbon, TOC, etc.) are used to express the pollution concentration. The magnitude of these parameters, especially COD, gives an estimate about the potential ozone reactivity. In addition to COD and TOC (this latter more commonly used in natural water), other parameters are employed to measure the degree of pollution. Among these parameters can be listed biological oxygen demand (BOD) and the measurement of wastewater absorptivity in the UV-C region, specifically at 254 nm wavelength (A 254 ). Another parameter that can be used is the mean oxidation number of carbon (MOC) that combines the values of COD and TOC to yield more reliable data on pollution concentration (specially during oxidation processes) avoiding the difficulties that some refractory compounds to COD determination present. Methods to measure any of these parameters can be followed elsewhere with the aid of detailed protocols issued by APHA, DIN, etc. 79,80 Here, a short explanation of the importance and application in water and/or wastewater of these parameters is given. 6.3.1 THE CHEMICAL OXYGEN DEMAND There is no doubt COD is the most general parameter to follow the pollution concentration of water in a given physical, chemical, or even biological process treatment. COD, in addition, gives a quantitative measurement about the depth of any chemical or biological oxidation step in the treatment of wastewater. This parameter, therefore, has been continuously applied to kinetic studies in water and wastewater treatment (such as ozonation) because, as a difference of other parameters like TOC (see later), COD supplies information on the magnitude of oxidation steps. COD represents the amount of oxygen needed for complete mineralization of the matter present in water through chemical oxidation. Also, it is used as a general parameter to express the variation in pollution concentration in physical–chemical processes such as flocculation–coagulation–sedimentation, filtration, etc. Thus, pol- lution concentration is measured in terms of mg oxygen units per liter of water. The proportionality between pollution concentration and COD is obtained once the theoretical oxygen demand, ThOD, is accounted for. Thus, this latter parameter represents the amount of oxygen needed to remove 1 mg of pollution. Then, pollution concentration in mg/l is simply the ratio between COD and ThOD: (6.1) COD, however, has some limitations derived from the presence in water or waste- water of compounds totally or partially refractory to chemical oxidation with dichro- mate, the chemical oxidant generally used in the analytical method, or volatile com- pounds that, during COD analysis, stay in the gas phase (COD analysis implies reflux methods). Examples of these compounds can be cyclohexane, tetrachloroethylene, pyridine, potassium cyanide, nitrate, etc. 81 Another problem stems from the contrary situation: the presence of compounds that consume dichromate but should not be C mg L COD mgO L ThOD mgO mg 2 2 () = () () [...]... CRC Press LLC 1 hT ∫ hT 0 Cgs (6. 16) TABLE 6. 5 Data on Henry Constant and Volumetric Mass Transfer Coefficient Corresponded to Ozone- Buffered Water and Ozone- Tomato Wastewater Systemsa Ozone System Ozone- buffered water Ozone- buffered water Ozone- buffered water Ozone wastewater Ozone wastewater Ozone wastewater Ozone wastewater He ؋ 10 6 System Characteristics pH 7, 12ºC, I = 0.01 M, Phosphate buffer pH... ▫=3 0-9 0 From Beltrán, F.J., García-Araya, J.F., and Álvarez, P., pH Sequential ozonation of domestic and wine distillery wastewater, Water Res., 35, 929–9 36, 2001 With permission Copyright 2001 Elsevier Press 1.0 b (Simple ozonation) b-a-b a-b-a b-a-b-a-b a-b-a-b COD/CODo 0.8 0 .6 0.4 a = acid cycle b = basic cycle 0.2 0.0 0 50 100 150 Time (min) 200 FIGURE 6. 5 Single and sequential ozonation of table... 20005, Am Water Works Assoc., Denver, CO, 17– 86, 19 86 4 Jekel, M., Flocculation effects of ozone, Ozone Sci Eng., 16, 55 66 , 1994 5 Dussert, B.W and Kovacic, S.L., Impact of drinking water preozonation on activated carbon quality and performance, Ozone Sci Eng., 1–12, 1997 6 Croll, B.T., The installation of GAC and ozone surface water treatment plants in Anglian water, Ozone Sci Eng., 1–18, 19 96 7 Lin,... post-treatment for ozonated water, Ozone Sci Eng., 24, 369 –378, 2002 ©2004 CRC Press LLC 63 Arslan-Alaton, I and Balcioglu A.K., Biodegradability assessment of ozonated raw and biotreated pharmaceutical wastewater, Arch Environ Contam Toxicol., 43, 425–431, 2002 64 Zenaitis, M.G., Sandhu, H., and Duff, S.J.B., Combined biological and ozone treatment of log yard run-off, Water Res., 36, 2053–2 061 , 2002 65 Deleris,... of petrochemical wastewater using ozonation and BAC advanced treatment system, Water Res., 35, 69 9–704, 2001 8 Roy-Arcand, L and Archibald, F.S., Ozonation as a treatment for mechanical and chemical pulp mill effluents, Ozone Sci Eng., 18, 363 –384, 19 96 9 Kamiya, T and Hirotsuji, J., New combined system of biological process and intermittent ozonation for advanced wastewater treatment, Water Sci Technol.,... organic matter ozone diffuses slower than in organic-free water On the other hand, the ozone solubility also depends on the organic matter present in the wastewater (see Chapter 5) However, as shown below (Section 6. 6.2), values of the Henry law constant determined by absorbing ozone in a wastewater do not differ too much from those in organic-free water. 92,93 Then, for calculation purposes, the ozone solubility... Phosphate–carbonate buffer Tomato wastewater, COD = 300 mgL–1, pH = 6. 5–7.8, 17–18ºC, 20 Lh–1 Tomato wastewater, COD = 500 mgL–1, pH = 6. 5–7.8, 17–18ºC, 35 Lh–1 Tomato wastewater, COD = 500 mgL–1, pH = 6. 5–7.8, 17–18ºC, 35 Lh–1 Domestic wastewater, COD = 300 mgL–1, pH 7.5, 20ºC kLa ؋ 102 Reference 9.14 93 11.75 93 8.49 1.05 93 7 .66 × 1 06 b 5.91 × 1 06 92 7.05b 6. 99 × 10–2 92 9.95c 92 7 .60 c 90 a He: Henry’s law... Rivas, F.J., Beltrán, F.J., and Gimeno, O., Joint treatment of wastewater from table olive processing and urban wastewater Integrated ozonation-aerobic oxidation, Chem Eng Technol., 23, 177–181, 2000 46 Rivas, F.J et al., Two step wastewater treatment: Sequential ozonation-aerobic biodegradation, Ozone Sci Eng., 22, 61 7 63 6, 2000 47 Carini, D et al., Ozonation as pre-treatment step for the biological batch... possible cases are treated: ozonation of wastewater in the fast and slow kinetic regimes In both of these cases, ozonation is represented by Reaction (6. 5) In Chapter 11, kinetic modeling is presented by considering both Reaction (6. 5) and Reaction (6. 6) 6. 6.3.1 Fast Kinetic Regime (High COD)* The absence of dissolved ozone, reaction factors higher than unity, and Hatta numbers higher than 3 (see also... solution for the problem of sludge disposal, Water Sci Technol., 46, 63 –70, 2002 66 Balcioglu, I.A and Ötker, M., Treatment of pharmaceutical wastewater containing antibiotics by O3 and O3/H2O2 processes, Chemosphere, 50, 85–95, 2003 67 Alvares, A.B.C., Diaper, C., and Parsons, A., Partial oxidation by ozone to remove recalcitrance from wastewaters-A review, Environ Technol., 22, 409–427, 2001 68 Hoigné, . basic cycle b (Simple ozonation) b-a-b a-b-a b-a-b-a-b a-b-a-b ©2004 CRC Press LLC Figure 6. 5, similar results can be observed for wastewater from a table olive pro- duction factory, although the. acidic-alkaline cycles, min: ∇=12 0-0 , ᭛= 0-1 20 ∆=1 0-1 10, ⅙=2 0-1 00, ▫=3 0-9 0. From Beltrán, F.J., García-Araya, J.F., and Álvarez, P., pH Sequential ozonation of domestic and wine distillery wastewater, . kinetic regime ozone direct reactions, while low polluted wastewater ozonation develops through slow kinetic regime ozone indirect reactions. 6. 3 CHARACTERIZATION OF WASTEWATER Through wastewater characterization,